The certification of the mass concentration of C-reactive protein in human serum : certified reference material ERM®-DA474/IFCC

This report describes the production of ERM-DA474/IFCC, a human serum material certified for C-reactive protein mass concentration. The material has been produced following ISO Guide 34:2009 [1]. Serum was produced from blood collected in 4 blood collection centres according to a procedure ensuring that it was obtained from healthy donors, and that the lipid content of the serum was low. The serum was processed, spiked with C-reactive protein, ampouled and frozen. Between unit-heterogeneity has been quantified and stability during dispatch and storage have been assessed in accordance with ISO Guide 35:2006 [2]. The material was characterised by an intercomparison among laboratories of demonstrated competence. Technically invalid results were removed but no outlier was eliminated on statistical grounds only. Uncertainties of the certified value were calculated in compliance with the Guide to the Expression of Uncertainty in Measurement (GUM) [3] and include uncertainties related to possible heterogeneity and instability and to characterisation. The material is intended for the calibration of immunoassays. As any reference material, it can also be used for control charts or validation studies. The CRM is available in glass ampoules containing 1 mL of human serum closed under argon atmosphere. The minimum amount of sample to be used is 20 μL. The CRM has been accepted as European Reference Material (ERM®) after peer evaluation by the partners of the European Reference Materials consortium.